The aim of biomedical research is to gain a better understanding of human physiology and to use this knowledge to prevent, treat or cure human diseases. Due to practical and ethical barriers to the experimentation on human subjects, many studies are conducted on small animal models, such as the mouse. Animal models of these human diseases are therefore needed.
For example, in the United States, around 20,000 patients are annually newly diagnosed with multiple myeloma (MM), a mostly incurable malignancy of antibody-secreting terminally differentiated B cells (Hideshima et al., 2007, Nat Rev Cancer. 7:585-98; Kuehl and Bergsagel, 2002, Nat Rev Cancer. 2:175-87). MM is characterized by the infiltration of malignant plasma cells in the bone marrow (BM) and clinical manifestations include bone disease, hypercalcemia, cytopenia, renal dysfunction, and peripheral neuropathy (Hideshima et al., 2007, Nat Rev Cancer. 7:585-98; Kuehl and Bergsagel, 2002, Nat Rev Cancer. 2:175-87). In most cases, MM is preceded by a premalignant condition called monoclonal gammopathy of undetermined significance (MGUS) that affects around 3% of persons older than 50 years (Landgren et al., 2009, Blood 113:5412-7). Complex heterogeneous genetic abnormalities characterize MM cells including changes in the karyotype as well as IgH translocations (Kuehl and Bergsagel, 2002, Nat Rev Cancer. 2:175-87; Zhan et al., 2006, Blood 108:2020-8). Plasma cell clones that are amplified in MGUS are thought to have genetic and phenotypic profiles similar to myelomatous plasma cells (Chng et al., 2005, Blood 106:2156-61; Fonseca et al., 2002, Blood 100:1417-24; Kaufmann et al., 2004, Leukemia. 18:1879-82). While mutations in cyclin D genes have been suggested to drive development of MM, the potential contributions of other factors have not been conclusively demonstrated (Bergsagel et al., 2005, Blood 106:296-303). Nonetheless, heritable genetic alterations are not the sole determinants of the behavior of MM cells. Instead, resistance towards drugs and aberrant biological responses towards cytokines are strongly influenced by interactions with the microenvironment offering an opportunity to develop novel therapeutics.
Like many other tumors, MM is characterized by heterogeneous cell populations strongly interacting with non-malignant stroma cells that create a supportive environment (De Raeve and Vanderkerken, 2005, Histol Histopathol. 20:1227-50; Dhodapkar, 2009, Am J Hematol. 84:395-6). The BM microenvironment for MM cells consists of a diverse extracellular matrix (ECM) and of cellular components of both hematopoietic and non-hematopoietic origin. While the BM provides a protected environment for normal hematopoiesis, the interaction of MM cells with ECM proteins and accessory cells plays a crucial role in MM pathogenesis (De Raeve and Vanderkerken, 2005, Histol Histopathol. 20:1227-50; Dhodapkar, 2009, Am J. Hematol. 84:395-6; Hideshima et al., 2007, Nat Rev Cancer. 7:585-98). Stroma cells, myeloid cells, osteoclasts, and osteoblasts produce growth factors such as interleukin 6 (IL-6), B-cell activating factor (BAFF), fibroblast growth factor, and stroma cell-derived factor 1a that activate signal pathways mediating migration, survival, and growth of MM cells. In particular, IL-6 produced by stroma cells, osteoclasts, and myeloid cells seems to be a crucial factor in the early stages and for pathogenesis of MM (De Raeve and Vanderkerken, 2005, Histol Histopathol. 20:1227-50). Similarly, upon interaction with MM cells, osteoclasts and dendritic cells produce BAFF and/or a proliferation-inducing ligand (APRIL) providing anti-apoptotic signals that also increase drug resistance (De Raeve and Vanderkerken, 2005, Histol Histopathol. 20:1227-50; Kukreja et al., 2006, J Exp Med. 203:1859-65).
The major events in cancer pathogenesis—uncontrolled proliferation, survival and spread of the malignant cells—depend on specific combinations of supportive cell types and soluble factors present in microenvironmental niches. Mouse models play an important role in characterizing key aspects of the driving forces of malignant transformation and disease in humans. However, they rarely represent the genetic complexity and clinicopathologic characteristics of human disease. While xenotransplantation of human tumors into immunocompromised mice has been extensively employed, reliable engraftment has typically been feasible only with highly aggressive tumors or cell lines.
The best models currently available to grow human tumor cells are severely immunodeficient mice that lack B cells, T cells, and NK cells. In the case of MM, engraftment of primary myeloma cells into these mice has been unsuccessful, but primary myeloma cells are able to engraft human fetal bone pieces upon co-transplantation into immunocompromised mice (Yaccoby et al., 1998, Blood 92:2908-13). In this model MM cells are found in the human bone, but are not detected in the mouse bone or in the periphery demonstrating high residual xenorejection and a need for the human BM microenvironment (Yaccoby et al., 1998, Blood 92:2908-13; Yaccoby and Epstein, 1999, Blood 94:3576-82). Proving its potential as in vivo model for MM, it was recently demonstrated that NOD/Scid/γc−/− mice allow the engraftment of several MM cell lines (Dewan et al., 2004, Cancer Sci. 95:564-8; Miyakawa et al., 2004, Biochem Biophys Res Commun. 313:258-62). However, even those mouse models with low xenorejection have constricted growth environments by virtue of a large number of factors that do not cross species barriers but are essential to support growth and survival of transformed cells (Manz, 2007). In vivo models that allow us to probe the complex pathogenic interplay between the tumor and its environment will be essential to design new drugs and therapies.
Therefore there is an unmet need to develop humanized non-human animals and methods to reliably grow and study human hematopoietic cells, including primary human hematopoietic tumor cells in mice. The present invention addresses these unmet needs in the art.